Remove the stems from the serrano peppers and place the serranos (including seeds), the red onion, half the cilantro, and half the tomatoes into a food processor; process until smooth. Pour in the rice vinegar and olive oil; pulse until smooth.
Stir together the remaining cilantro, the remaining tomatoes, the mango, green bell pepper, corn, cumin, and sugar in a medium bowl. Stir in the serrano pepper mixture. Season to taste with salt and black pepper. Chill for 1 hour before serving.